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# Measuring lab

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Procedures to all the measuring exercises performed in the lab.

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### Measuring lab

1. 1. Procedure A: Measuring Size DistributionIntroduction:The objective of this procedure is to measure a large sample and obtain a largenumber of data, so you can statistically process, analyze and evaluate your data.By deciding which leaves to measure and how, you will undoubtedly influence onthe quality of your results. This will introduce error and uncertainty in your data,which will allow you to calculate and graph error bars and standard deviation.Procedure:The procedure to obtain length measurements is simple: 1. Decide and choose which leaves to measure, making sure that the sample is representative of the whole plant. That means, don’t choose leaves only from the top or the bottom. 2. Use a ruler to measure the size of a leave. Whether you decide to measure length or width, or both, is irrelevant, but you should be consistent in the way you measure. Each leaf should be measured exactly the same way. 3. Build a table to record your measurements. 4. Record any observations.
2. 2. Procedure B: Measuring Mass Distribution:Introduction:The objective of this procedure is to measure a large sample and obtain a largenumber of data, so you can statistically process, analyze and evaluate your data.By deciding which beans to measure and how, you will undoubtedly influence onthe quality of your results. This will introduce error and uncertainty in your data,which will allow you to calculate and graph error bars and standard deviation.Procedure:To measure mass is simple: 1. Turn on the balance and wait for its self-calibration for about a minute. If the number on the scale is not zero, press the re-zero button once. 2. Put a bean on the scale and wait for the reading to stabilize. Record the reading. 3. Remove the bean without pressing on the balance. Wait for the balance to go back to zero by itself before putting on a new bean. 4. Make sure there are no air currents over the balance (if you are near a door, if people walk by or if you move things quickly over the balance) since this will give you wrong readings. 5. Repeat the procedure for 50 beans. 6. Record your measurements and all other observations.
3. 3. Procedure C: Measuring Concentration and Preparing SolutionsIntroduction:The objective of this procedure is to investigate how error can propagate whencombining two measurements. Every time we have to measure something, weintroduce error to our measurements from different sources. Since thepreparation of a solution implies two measurements, mass and volume, we musttake into account and calculate the error and uncertainty that bothmeasurements contribute to the total. Another aspect to take into considerationis the calculation of concentration. The concentration of a solution is commonlyexpressed in moles per liter, mol/l or M. Hence a solution of NaCl 0.7M means thatthe concentration of NaCl is that of 0.7moles of NaCl per every liter of water. Inorder to calculate the molarity of a solution, you need to know the number ofmoles of solute and the total volume of the solution: 1. Use the chemical formula to determine the number of each type of atom present in the compound. Ex.: Na2CO3 2. Multiply the atomic weight (from the periodic table) of each element by the number of atoms of that element present in the compound. Ex.: Na: 2 x 23.0= 46.0 ; C: 1 x 12.0 =12.0 ; O: 3 x 16.0= 48.0 3. Add it all together and put units of grams/mole after the number. Ex.: molar mass = 46.0 + 12.0 + 48.0 = 106.0 g/mol 4. Calculate the number of moles present by dividing the molar mass bythe amount of grams of solute. Ex.: Na2CO3: 1.2ggrams will cancel out Na2CO3: 0.011 mol 106.0 g/mol 4. Calculate the number of liters of solution present. Ex.: 0.15l 5. Divide the number of moles of solute by the number of liters of solution. Ex.: Molarity (M) = 0.011 mol = 0.073 mol/l or 0.073M 0.15lProcedure: 1. Using the information and the equations above, calculate the amount of water and the amount of salt (NaCl) you will need to prepare a solution of NaCl 1M. 2. Measure the volume of water carefully and transfer to a plastic cup. 3. Weigh the amount of salt carefully and transfer it to a plastic cup. 4. Repeat the procedure for a solution of NaCl 2M. 5. Record your data, calculations, and all observations.